Television camera system with a sinusoidally varying indexing signal

ABSTRACT

Light from a scene is directed through the faceplate of an image pickup device having an electron gun operative to produce an electron beam. The light impinges upon a layered target structure including a photoconductor and a conductive signal electrode. The target structure is comprised of a first and second plurality of spaced parallel elongated areas. The widths of the first and second plurality of spaced parallel elongated areas in the direction of scanning differing cyclically from smaller widths to progressively larger widths back to smaller widths of varying conductivity such that the scanning of an electron beam across the target structure produces a composite video signal containing a color information signal representative of the color of the image formed on the target and an index signal whose frequency is less than the color information signal and is representative of the first and second plurality of spaced parallel elongated areas. Means are provided for separating the video signal information from the index signal.

United States Patent [191 Pritchard et al.

[54] TELEVISION CAMERA SYSTEM WITH A SINUSOIDALLY VARYING INDEXING SIGNAL [75] Inventors: Dalton Harold Pritchard; Walter Edgar Sepp, both of Princeton, NJ.

[73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Mar. 17, 11972 [21] Appl. No.: 235,497

[52] US. Cl. ..178/5.4 ST [51] Int. Cl. ..H04n 9/06 [58] Field of Search ..l78/5.4 ST

[56] References Cited UNITED STATES PATENTS 3,566,018 2/1971 Macovski ..l78/5.4 ST 3,575,548 4/1971 Kurokawa ..l78/5.4 ST

Primary Examiner-Robert L. Griffin Assistant Examiner-George G. Stellar Att0rneyEugene M. Whitacre et al.

l6| ELECTRON SCANNING BEAM DIRECTION I48 TRANSPARENT cowoucnvr LAYER [451 May 22,1973

[57] ABSTRACT Light from a scene is directed through the faceplate of an image pickup device having an electron gun operative to produce an electron beam. The light impinges upon a layered target structure including a photdconductor and a conductive signal electrode. The target structure is comprised of a first and second plurality of spaced parallel elongated areas. The widths of the first and second plurality of spaced parallel elongated areas in the direction of scanning differing cyclically from smaller widths to progressively larger widths back to smaller widths of varying conductivity such that the scanning of an electron beam across the target structure produces a composite video signal containing a color information signal representative of the color of the image formed on the target and an index signal whose frequency is less than the color information signal and is representative of the first and second plurality of spaced parallel elongated areas. Means are provided for separating the video signal information from the index signal.

24 Claims, 13 Drawing Figures I06 PHOTOCONDUCTOR TARGET OUTPUT 155 SUBSTRATE PATENTEB III.Y22I975 3 735,Q28

sum 2 [IF 7 I 55 SUBSTRATE I48 TRANSPARENT CONDUCTIVE LAYER I53 COLOR FILTER STRIPS I6I ELECTRON SCANNING BEAM DIRECTION PATENTEU 243.! 2 21975 SHEET 3 OF 7 Em; Em: Q28 B Q Ema? 8 $55 ma; 5% $55 55828 E was 553% 5 k H 85 m o y m A F I F q PAIENTEN III-N 22 I975 sNEEI N NE 7 I- I6I ELECTRON B I M SCAN DIRECTION O M O WV E w M W 6 I mw mm S E 5WD OW OM 1N O o O a I 0mm Law OM AN 45 m T 2P8 5 E PATENTEUHAYZZ m5 sum 5 [1r 7 TELEVISION CAMERA SYSTEM WITH A SINUSOIDALLY VARYING INDEXING SIGNAL BACKGROUND OF THE INVENTION This invention relates to television camera systems and more particularly, to a television camera system for encoding a plurality of information signals as phase and amplitude modulation of a carrier wave with an integrally related indexing signal derived from scanning. One example of the use of this invention is in singletube color encoding camera systems.

One way to encode a plurality of colors with a single image pickup device of a television camera is to spatially encode the colors impinging on the photosensitive electrode of the pickup device. The encoding may be accomplished by utilizing a spatial color encoding filter disposed in the optical path to the image pickup device to spatially separate the different colored light passing therethrough. The filter may be adjacent the transparent conductive electrode of the pickup device in which case a relatively simple optical system is utilized to image the scene onto the photoconductor. Alternatively, it may be desirable to place the encoding filter in the optical path some distance from the photoconductor in which case a relay lens assembly is utilized to image the scene and the encoding filter pattern onto the photoconductor.

One type of spatial color encoding filter comprises a single color encoding grating including a repeating pattern of several different color stripes. Colored light encoded by a filter of this type produces an electrical signal containing colored light information as phase and amplitude modulation of a suppressed carrier wave as the photoconductor is scanned. The carrier wave frequency is determined by the number of repeating color stripe groups and the rate of scanning. The phase of a particular color representative signal relative to the other colors is determined by the position of its color encoding stripe within the group.

A phase and amplitude modulation color encoding system of this type when the transmissivity of the encoding filters are equal, has the advantage of generating no subcarrier when a gray or white scene is present. This results in maximum dynamic range of the pickup device and inherent color balance. The system also has the ability of containing information representative of a plurality of colors within a relatively narrow band of frequencies enabling use of other portions of the available frequency spectrum of the pickup device for the luminance representative information of the scene.

However, in a phase modulation color encoding system it is necessary to provide a reference or indexing signal which can be utilized to demodulate the carrier wave and sidebands containing the color information. Nonlinearities in this scanning system make it desirable to provide an indexing signal which accompanies the phase modulated color representative carrier wave so that both are affected similarly by any system nonlinearities and proper demodulation of the carrier wave may be achieved.

A variety of means exists for generating an indexing signal in specific relationship to a color signal produced by scanning of an image encoded by a stripe filter. One such scheme utilizes a separate light source to illuminate an additional grating imaged on the photosensitive material of the image pickup device.

LII

If the index frequency is at the color carrier frequency,

extraction of the index signal becomes difficult. When the index frequency is close to the color carrier frequency, the index frequency experiences phase errors in demodulating the color carrier. This error is known as color pulling. The problem of color pulling is more fully described in US. Pat. No. 2,962,546, Color Television Indexing Apparatus."

Other inherent disadvantages associated with the above-mentioned systems include loss of signal resolution when the produced index signal is at a higher frequency than the color carrier frequency due to the limited optical response of the pickup device.

In copending application, Ser. No. 235,587, filed for JJ. Brandinger and entitled Television Camera System With Enhanced Frequency Response, the color pulling problem was solved by providing an indexing signal at frequencies above the optical resolution of the image pickup device. Although solving the color pulling problem, an ambiguity problem was introduced which required additional structure and ambiguity resolving circuitry.

SUMMARY OF THE INVENTION A television camera system according to the invention includes an image pickup device comprising a faceplate, an electron gun operative to produce an electron beam, an encoding filter comprising groups of elongated parallel stripes, each stripe within a group having a different spectral response to light passing therethrough, a layered target structure including a conductive signal electrode and a photoconductor layer that is addressed by the electron beam. A circuit is provided between the signal electrode and the electron gun to derive a composite electrical signal that is representative of light from an image directed upon the target. The composite electrical signal includes a video information signal which is representative of the image formed on the target; an electrical carrier signal having a frequency determined by the number of groups of the elongated parallel stripes scanned by the electron beam in a given time; and an index signal having a frequency lower than the carrier signal. The index signal is generated by a special target structure which includes a first plurality of spaced elongated parallel areas separated by a second plurality of spaced elongated parallel areas. The number of the areas in either of the plurality of areas being selected to produce current impulses of a frequency above the frequency of the electrical carrier signal when the target is scanned by the electron beam traversely to the length of the areas. The width dimensions of the areas of one of the plurality of areas measured in the direction of electron beam scanning differ in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate which when scanned by the electron beam is at a frequency of the index signal. A

means is provided to separate the index signal from the composite electrical signal.

The above invention allows an indexing signal to be present when no light is impinging upon the target structure. An index signal is produced whose frequency is less than the color carrier frequency but composed of component current impulses whose frequencies may be above the optical frequency response of the image pickup device thereby reducing the color pulling problem without associated ambiguity problem.

A more detailed description of the invention is given in the following specification and accompanying drawings of which:

FIG. 1a is a block diagram of a single tube color television camera system embodying the invention;

FIG. 1b is a curve representative of the color, brightness and index signal frequency spectrum of the system shown in FIG. la;

FIG. 2 is a plan view of an image pickup device target configuration in accordance with one embodiment of the invention and useful in the system of FIG. 1a;

FIG. 3a is a cross-sectional view of a portion of the target configuration shown in FIG. 2;

FIG. 3b contains curves representative of transmission characteristics of different color encoding filters used in conjunction with the target structure of FIG. 2;

FIG. 30 is a top view of a color encoding filter the stripes of which are angularly disposed to the direction of scan of a scanning beam;

FIG. 4a is a diagram representing the deflection characteristics of an electron beam as it crosses the target of the image pickup device shown in FIGS. 2 and 3a;

FIG. 4b contains curves representing the optical and electrical response of a vidicon tube embodying the invention;

FIGS. Sa-f are curves for describing the generation of a sinusoidal index waveform obtained from the structure of FIG. 2;

FIG. 6 is a diagram showing the beat cancellation circuitry of FIG. la in more detail;

FIG. 7 is a block diagram of system circuitry for direct heterodyne conversion to standard NTSC color form; and

FIGS. 8a and 8b are cross-sectional views of the target structure showing different embodiments of the invention.

DESCRIPTION OF THE INVENTION FIG. 1a is a block diagram of a single tube color camera system for producing color representative signals and a sinusoidal index signal. Light rays 102 from an object 101 are directed by an objective lens 103 to the faceplate 155 of an image pickup device 107. Adjacent the inner surface of faceplate 155 are a color encoding filter 153, an indexing target structure 105 and a photoconductor 106. Image pickup device 107 may be a vidicon, for example, which operates in a conventional manner with the exception of the index signal producing portion of the target structure, which will be described herein.

Synchronizing signals are coupled from a synchronizing generator 11 1 to deflection circuits 109 for producing suitable deflection waves which are in turn coupled to the vertical and horizontal deflection coils 110 of image pickup device 107, for causing the electron beam to scan a raster over the target structure at conventional line and field scanning rates.

The color encoding filter 153 and indexing structure adjacent the faceplate 155 are constructed so that as the electron beam of image pickup device 107 is scanned over the photoconductor 106, a composite electrical signal including luminance information, encoded color or chrominance information, an ambiguity resolving pulse and an index signal is obtained from output terminal 108. Operation of the indexing structure will be described in conjunction with FIGS. 2, 3a, 4a, 4b and 5.

The composite signal from output terminal 108 is amplified by preamplifier 113 and then coupled to three separate bandpass filters 115, 117 and 119.

FIG. 1b is a curve representative of the composite signal developed at the terminal 108. The curve 112 shows that the luminance information signals occupy the spectrum from 0 to 3.5 MHz. The curve 114 indicates that the chrominance information frequency spectrum extends from 3.5 MHz to 4.5 MHz centered around 4.0 MHz. Curves 116-1 and 116-2 show the frequencies of high frequency indexing signals which are generated, and interact to develop the approximately sinusoidally varying index frequency represented by curve 116-3.

The first filter is a low-pass filter which has a bandwidth extending from 0 to approximately 3.5 MHz. This filter is used to separate the luminance information portion from the composite signal and is coupled to beat cancellation circuit 118 which is also coupled to preamplifier 1 13. The beat cancellation circuit 118 is used to eliminate the beat produced in the luminance bandwidth by the generation of the index signal. The operation of the beat cancellation circuit will be discussed in conjunction with FIG. 6.

Bandpass filter 117 separates the color information components from the luminance and index components of the composite signal. Bandpass filter 117 has a center frequency of 4.0 MHz and a bandpassof 1 MHz. The frequency of the suppressed color carrier wave is determined by the number of red, green and blue color stripe groups of color encoding filter 153 scanned in the time of a horizontal scan line.

The index signal is separated from the composite signal by bandpass filter 119 having a center frequency of 1.33 MHz and a bandpass of 1 MHz. The production of a 1.33 MHz sinusoidally varying index signal from index structure 105, will be described in conjunction with FIGS. 2, 3a, 4a, 4b and 5. The index signal obtained from filter 119 is coupled to a limiter 123 which produces a constant amplitude of index signal. This limited index signal is then coupled from limiter 123 to frequency multiplier 131. In this embodiment of the invention where the index frequency was chosen as 1.33 MHz, frequency multiplier 131 multiplies the index frequency by three to produce a frequency of 4 MHz a frequency equal to the color carrier frequency. The index signal from frequency multiplier 131 is then coupled to phase shifter 135. Phase shifter generates three index signals which are phase related to the chrominance signal from bandpass filter 117 such that they can serve to demodulate the color representative carrier wave.

The chrominance information obtained from filter 117 is amplified in amplifier 121 and then is coupled to a red synchronous detector 125, blue synchronous detector 127 and a green synchronous detector 129. Detectors 125, 127 and 129 are controlled by the signals from phase shifter 135. Since the chrominance information is phase related to the index signal, phase shifter 135 produces the proper signals to detect red, blue and green information of the object 101 from the composite chrominance signal.

The detected red information obtained from synchronous detector 125 is coupled to a low-pass filter 137. The blue information signal is coupled to a lowpass filter 139 and the green information signal is coupled to low-pass filter 141. Low-pass filters 137, 139 and 141 each have a bandpass of approximately 500 R112. The synchronous detectors 125, 127 and 129 detect signals representative of red, blue and green information respectively, but they can alternatively be used to detect signals representative of magenta, yellow and cyan.

The luminance signal from low-pass filter 115 is then coupled to a matrix and encoder circuit 143 where it is combined with the red, blue and green signals from low-pass filters 137, 139 and 141. The color representative signals from low-pass filters 137, 139 and 141, the luminance signal obtained from beat cancellation circuit 118 and synchronizing information from the synchronizing generator 111 are combined in the matrix and encoder circuit 143 to produce a composite color television signal at output terminal 147 which may be suitable for transmission or for processing by video and color circuits of a television receiver.

The image pickup tube target assembly is shown in FIG. 2. FIG. 2 is a perspective view, not drawn to scale, of the target assembly of FIG. 1a.

The target assembly in FIG. 2 is comprised of four separate layers. The first layer is a substrate 155 which is a transparent material and can be the faceplate of a vidicon. The second layer is the color encoding filter and is composed of color stripes 153 (e.g., dichroic filters, organic dyes, or Fabry Pierot filters).

FIG. 3b represents transmission characteristics of color encoding filters. These filters can have the property of transmitting only red, green or blue light. Such filters would have the transmission characteristics represented by curves 134, 136 and 136, respectively. Alternatively, the color filters can be of the type that allow transmission of cyan, magenta and yellow represented by curves 140, 142 and 144, respectively.

The color filters are deposited upon substrate 155 by techniques of photoprocessing, printing deposition or evaporation. The color stripes spatially separate the color information and are arranged parallel to each other and in groups of three (i.e., red, green and blue (RGB) stripes representing a single color group). The repetition of these color groups in the direction of the electron beam scan 161 along with the scan velocity determine the frequency of the electrical color carrier generated. For example, when l t color groups are used, a color subcarrier frequency of about 3.6 MHz is produced using NTSC television horizontal scanning rates.

FIG. 3c illustrates the angular positioning of the stripes of a color encoding filter to the direction of horizontal scan of an electron beam of a vidicon tube. The color filter stripes 153 can be angularly disposed to the electron beam 162 direction of scanning as taught by RD. Kell, US. Pat. No. 2,733,291, thereby allowing the frequency of the electrical color carrier generated to be reduced, depending upon the angle of the color filter stripes to the electron beam while maintaining the same number of color filter stripes per unit distance.

The third layer of the assembly shown in FIG. 2 is a transparent conductor target area 1 disposed over the color filter stripes. The conductor area 148 has a first plurality of spaced parallel elongated areas 149 separated by a second plurality of spaced parallel elongated areas 151 to produce an array of alternating conductive stripes 151 and nonconducting spaces 149. The conducting and nonconducting areas are parallel to the color filter stripes to within 18 milliradians or about 001 to maintain colorimetry to NT SC standards. The transparent conductive index stripes 151 are electrically connected together and require only a single terminal external to the image pickup tube. The fabrication of the transparent conductive index stripes 151 and slots 149 can be done by any suitable method, i.e., photoresist processing. The target assembly will produce an index signal when scanned by an electron beam, the index signal being used to decode the color information contained as phase modulation of the color representative carrier wave. The detection of the wave representative of the nonconducting areas, due to the decreased signal-to-noise ratio, becomes more difficult as the width of the nonconducting areas get smaller.

The fourth layer with reference to FIG. 3a consists of a photoconductor 1116 deposited over the transparent conductor 1.

Operation of the image pickup device 107 of FIG. 1 can be explained with reference to FIG. 3a. FIG. 3a is a cross-sectional view of the target assembly of FIG. 1a.

Light 163 passes through transparent substrate 155 and impinges upon the color filter stripes 153. The light is spatially separated by the filters and impinges upon the transparent conductive stripes 151. Assuming there is no loss in transparent conductive stripes 151, the light continues until it impinges upon the photoconductor 166 where the resistance of the photoconductor 1 is changed by the amount of light that is present. The electron beam 161 charges the photoconductive layer to about the potential of the image pickup tube cathode. The transparent conductive stripes 151 are maintained at a potential which is positive relative to the cathode. The amount of charge at any elemental area of the photoconductor which leaks to the transparent conductive stripes 151 is determined by the resistance of the photoconductor, which in turn is determined by the amount of light image thereon. The amount of charge deposited by the electron beam 161 during the next scanning is determined by how much leaked off since the last scanning. This amount of beam current corresponds to the amount of incident light at that particular area and causes a current to flow through a load impedance shown as a resistor R connected between the transparent conductive stripes 151 and the voltage source +V.

When the electron beam 161 scans over the nonconducting areas 149 in the conductive area 148 with associative conductive stripes 151, no signal is produced representing a color, however, a signal representing the nonconducting area 149 is produced. A signal referred to as dark current is produced whether light is present or not. Therefore, when the electron beam scans across the total target area, a current is produced that varies with the amount of light present where a transparent conductive image stripe and light are present and will also represent the difference between current produced when a beam strikes the conducting and nonconducting areas. This therefore produces three signal components: a first signal representative of the intensity of the light which varies the photoconductive resistance (which is the luminance portion of the composite signal); a second signal representative of the spatial position of where that light was present and determined by the color filters (this representing the chrominance signal) and a third signal, the index signal, composed of a series of square waves of varying periodicity during each line scan produced by the alternating conducting and nonconducting areas producing the index signal whose intensity varies also with the amount of light present.

FIG. 4a is a diagram representing the deflection characteristics of an electron beam as it crosses a nonconducting area 149 of the target and indexing structure shown in FIG. 2. The electron beam deposits a negative charge on the photoconductor 106 overlying the nonconducting area 149 which is not easily dissipated to the conductive area 151. The negative charge on the photoconductor 106 overlying the adjacent conductive areas will be less in proportion to the amount of incident light in that area, and will be less even in the absence of light because of the leakage to the closely adjacent underlying conductive area 151. this leakage is referred to as dark current. Thus, as electron beam 161 scans over the portion of the photoconductor over the nonconducting area 149, the negative charge buildup in this area will repel the beam causing it to dwell longer on the portions of the photoconductor 106 overlying the edges of the conductive stripes 151. This action enhances the ability of the image pickup tube to resolve the slots 149 by a factor of at least 2 to 1 over the resolution of the equivalent optical image.

FIG. 4b is a diagram representing the electrical and optical response of a vidicon tube. Curve 152 represents the optical response of the tube, while curve 154 represents the detectable electrical response of a tube utilizing the applicants invention for producing an indexing signal. Experimental tests of standard one inch vidicons utilizing an antimony trisulfide photoconductor and having a modified striped transparent conductive electrode with the stripes at repetition rates of 500, l,000 and 2,000 lines per inch gave useful electrical index signals from 4.5 to 18 MHz. The ability to produce an electrical index signal beyond the optical resolution of the vidicon tube permits the useful optical resolution of the image pickup device to be used for the generation of video signals, and at the same time permits a generation of signals for indexing whose frequencies are near the limit or outside the limit of the optical frequency response of the device. The pickup device's ability to detect a visual image is improved due to the reduced scattering within the target structure.

In copending application Ser. No. 235,587 filed for J .J Brandinger, a slotted transparent conductor is provided which, when scanned by an electron beam, produces an indexing frequency above the optical frequency response of the image pickup device. It has been found that the higher an index frequency is chosen above the color carrier frequency, the less the error from color pulling. The system described in the referenced application reduces the color pulling problem but produces an ambiguity problem. A phase ambiguity choosing one of two phases present will exist when the index frequency is a multiple of the color carrier frequency. No phase ambiguity exists when a submultiple of the color carrier is chosen as the index frequency. The ambiguity problem is resolved by adding special structure to the target and additional ambiguity resolving circuitry.

The present invention while using a slotted transparent conductor layer to provide the necessary high frequency pulses for avoiding the color pulling problem, also provides a substantially sinusoidal indexing signal whose frequency is at one-third the color carrier frequency. This thereby eliminates the ambiguity problem while still maintaining the virtues of high frequency indexing.

The f/3 indexing signal is produced by the non-linear interaction of two high frequency waves whereby an index signal is produced which approximates a sine wave.

As colored light passes through the target structure, complex color and high frequency waveforms are produced due to the conductive index stripes and the color filter stripes. When the two high frequency pulses are beat against each other, their difference product is an index signal that approximates a sine wave. The resultant index signal has little color pulling error.

FIG. 5a shows a curve representative of a wave whose frequency is one-third the color carrier frequency. A wave whose frequency is equal to the color carrier frequency, f, is shown in FIG. 5b. FIGS. 5c and 5d show waves whose frequencies are 6/3 and 7/3 the color carrier frequency, f. By superimposing the wave pattern shown by FIG. 5c with FIG. 5d, a sinusoidally varying wave pattern is generated and represented by FIG. 5e. The amount of time for each succeeding wave varies, and the frequency of variation is equal to the difference between frequency of occurrence of FIGS. 5c and 5d or equal to f/3.

The waveform of FIG. 5e represents the beat pattern that is formed when a photographic mask containing light and dark areas as shown in FIG. 5c has superimposed upon it a second mask containing light and dark areas as shown in FIG. 5d. The resultant superposition of these two patterns produces a light and dark beat pattern as shown in FIG. 5e. This pattern is photoetched onto the transparent conductor and produces the elongated spaced parallel conducting areas shown as 151 of FIG. 30. As an electron beam 161 moves across the transparent conductive stripes 151, an electrical index signal, approximately a sine wave, is generated by the difference frequency beat between the 7f/3 and 6 f/3 indexing pulses generated. The sinusoidally varying indexing signal is comprised of a fundamental component whose frequency is one-third the color carrier frequency and represented by FIG. 5f.

By picking the proper frequencies of the curves represented by FIGS. 50 and 5d, such that the difference between them is an exact submultiple of the color frequency, here being three, the resultant is a sine wave at one-third the color frequency.

FIG. 6 is a diagram showing in more detail, the beat cancellation circuitry represented by box 118 of FIG. 1a. The beat cancellation circuitry is used to eliminate the difference beat of 1.33 MHz that is produced in the generation of the sinusoidal index signal.

Inductor 118-1 and capacitor 118-2 are used as a series resonant filter to select a signal from preamplifier 1 13 whose frequency is 8 MHz. Inductor 1 18-3 and capacitor 118-4 are also used as a series resonant filter to select a signal from preamplifier 113 whose frequency is 9.33 MHz. The signals from these filters are coupled through a network comprised of diodes 118-5 and 118-6 and resistor 118-8 which allows positive excursions of current to pass and clamps the signal at a set level. The clamped signal is coupled through capacitor 118-7 and then coupled into a parallel resonant tank circuit comprised of capacitor 110-9, inductor 118-10 and variable resistor 118-11. The tank circuit is tuned to the difference beat frequency produced by the two signals coupled to it. Therefore, a signal whose frequency is 1.33 MHz is coupled from the output of the tank circuit to subtractor 118-12 where this beat frequency is removed from the luminance bandpass filter 115 by cancellation. The output of subtractor 118-12 contains luminance information free of the 1.33 MHz beat, which signal is then coupled to matrix and encoder circuits 143.

FIG. 7 is a block diagram of system circuitry for direct heterodyne conversion to standard NTSC color form. The composite signal from preamplifier 113 of FIG. 1a is coupled to a low-pass filter 201, a bandpass filter 202 which passes the chrominance signal and a bandpass filter 203 which passes the index signal. Lowpass filter 201 has a bandwidth extending from to approximately 3.5 Ml-lz. The output of this filter is coupled to beat cancellation circuit 118 where a beat signal produced in the generation of the index signal is removed from the luminance signal. The output of the beat cancellation circuitry 1 18 is coupled to adder 204. The chrominance portion of the signal is obtained from bandpass filter 202 which has a center frequency of 4.0 MHz and a bandpass of 1 MHz. The output of the chrominance filter 202 is fed into mixer 205. The index signal is obtained from bandpass filter 203 having a center frequency of 1.33 MHz and a bandpass of 1 MHz. The index signal from filter 203 is coupled to limiter 206 which produces a constant amplitude of index signal. This index sigial is then coupled from limiter 206 to frequency multiplier 207. In this embodiment of the invention where the index frequency was chosen as 1.33 MHz, frequency multiplier 207 multiples the index frequency by three to produce a frequency of 4 MHz, a frequency equal to the color carrier frequency. The index signal from frequency multiplier 207 is coupled to mixer 209. Crystal controlled oscillator 208 produces a carrier frequency of 3.58 MHz. The 3.58 MHz signal is then coupled to mixer 209 where it is heterodyned with the index frequency. The output of mixer 209 is a carrier frequency of 7.58 MHz (3.58 MHz 4 MHz). The mixer output of 209 is then coupled to mixer 205 where it is heterodyned with the chrominance information signal from bandpass filter 202. The output of mixer 205 is composed of a carrier frequency of 3.58 MHz modulated by the chrominance information. Mixer output 205 is then coupled to adder 204 where the luminance information is added to the carrier frequency. The output of 204 is a composite color signal translated to a 3.58 MHz carrier frequency containing luminance, chrominance and index information in standard NT SC color signal form for transmission.

An embodiment utilizing the invention is shown in FIG. 8a. The target structure is comprised of a faceplate 155, and color stripe filters 153. Adjacent the color stripe filters 153 are parallel nonconducting areas of constant width 149. Separating the nonconducting areas are parallel conducting areas of transparent conductor 151 whose width dimensions measured in the direction of scanning will differ in a progression from smaller to larger back to smaller at a cyclical rate. Disposed over the conducting and nonconducting areas 149 and 151 is photoconductor 100. When electron beam 161 scans across the two parallel areas, a sinusoidal varying index signal is produced.

An alternative to the above embodiment is shown in FIG. 0b. in this embodiment the parallel areas of transparent conductor 151 have a constant width while the nonconducting parallel areas 149 have widths varying cyclically in the direction of scanning.

Another embodiment of this invention includes a target and indexing structure utilizing a spectral encoding filter that is sensitive to electromagnetic radiation other than in the visible radiation spectrum. For example, silicon and germanium filters could be used to filter infrared radiation and display this radiation as a color on the viewing screen, each color corresponding to the different wavelength of radiation that has been filtered. Alternatively, multispectral filters can be selected to transmit difierent ranges of ultraviolet radiation or combinations of ultraviolet, visible and infrared radiation. The one requirement of the encoding filter for the above embodiments is that the spectral filters, when impinged by the proper radiation, change the sensitivity of the photoconductor, thereby changing its resistance which allows a current of varying amplitude to be passed through the transparent conductive index material according to the amplitude of the filtered radiation reaching the transparent conductor. The decoding apparatus is essentially the same as that used in the decoding of color and indexing information, while the luminance information could represent the actual luminance of the scene or the average radiation over a wide spectral range of the object being viewed.

What is claimed is:

1 A television camera system comprising:

an image pickup device including;

a transparent faceplate;

an electron gun operative to produce an electron beam;

an encoding filter comprising groups of elongated parallel stripes in each group having a different spectral response to light passing therethrough;

a layered target structure including a conductive signal electrode and a photoconductor layer addressed by said electron beam;

circuit means connected between said signal electrode and said electron gun to derive a composite electrical signal representative of light from an image directed upon said target, said composite electrical signal including video information signal representative of said image formed on said target, an electrical carrier signal having a frequency determined by the number of groups of said elongated parallel stripes scanned by said electron beam in a given time, and an index signal having a frequency lower than said carrier signal;

said target structure including a first plurality of spaced elongated parallel areas separated by a second plurality of spaced elongated parallel areas, the number of said areas in either of said plurality of areas being selected to produce current impulses of a frequency above the frequency of said electrical carrier signal when scanned by said electron beam traversely to the length of said areas, the

width dimensions of said areas in one of said plurality of areas measured in the direction of electron beam scanning differing in a progression from smaller widths to larger widths and back to smaller widths at a cyclical rate which when scanned by said electron beam is at the frequency of said index signal;

means coupled to said circuit means for separating said index signal from said composite electrical signal.

2. A television camera system according to claim 1 wherein the width dimensions in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is comprised of conducting material.

3. A television camera system according to claim 1 wherein the width dimensions measured in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is nonconductmg.

4. A television camera system according to claim 1 wherein:

said first plurality of areas is comprised of conducting material and said second plurality of areas is nonconducting, the width dimensions measured in the direction of scanning of said first and second plurality of areas differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate.

5. A television camera system according to claim 4 wherein said first plurality of spaced parallel elongated areas is said conductive signal electrode.

6. A television camera system according to claim 5 wherein said target structure and said encoding filter being supported adjacent said transparent faceplate so that light from an image passes through said faceplate and said encoding filter before impinging on said target, the stripes of said encoding filter being positioned parallel to said first and second plurality of spaced parallel elongated areas wherein the number of spaced parallel elongated areas of said first and second plurality of spaced parallel elongated areas for a given distance being greater than the number of groups of said elongated parallel stripes for the same distance;

said indexing signals frequency of variation determined by the number of said first and second spaced parallel elongated areas scanned by said electron beam in said given time; and

signal processing means coupled to said means and said circuit means and responsive to said index signal for processing said composite electrical signal to derive a plurality of color representative signals.

7. A television camera system according to claim 6 wherein said encoding filter is a color encoding filter comprising color groups of elongated parallel stripes for encoding red, green and blue light.

8. a television camera system according to claim 6 wherein:

said color encoding filter comprises color groups of elongated parallel dichroic stripes for encoding red, green and blue light.

9. A television camera system according to claim 7 wherein:

said color group is comprised of cyan, magenta and yellow parallel dichroic stripes.

10. A television camera system comprising:

an image pickup device including;

a transparent faceplate;

an electron gun operative to produce an electron beam;

an encoding filter comprising groups of elongated parallel stripes in each group having a different spectral response to light passing therethrough;

a layered target structure including a conductive signal electrode and a photoconductor layer addressed by said electron beam;

circuit means connected between said signal electrode and said electron gun to derive a composite electrical signal representative of light from an image directed upon said target, said composite electrical signal including video information signal representative of said image formed on said target, an electrical carrier signal having a frequency determined by the number of groups of said elongated parallel stripes scanned by said electron beam in a given time, and an index signal having a frequency lower than said carrier signal;

said target structure including a first plurality of spaced elongated parallel areas separated by a second plurality of spaced elongated parallel areas, the number of said areas in either of said plurality of areas being selected to produce current impulses of a frequency above the frequency of said electrical carrier signal when scanned by said electron beam traversely to the length of said areas, the width dimensions of said areas in one of said plurality of areas measured in the direction of electron beam scanning differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate which when scanned by said electron beam is at the frequency of said index signal;

said target structure and said encoding filter being supported adjacent said transparent faceplate so that light from an image passes through said faceplate and said encoding filter before impinging on said target, the stripes of said encoding filter being positioned parallel to said first and second plurality of spaced parallel elongated areas, the number of spaced parallel elongated areas of said first and second plurality of spaced parallel elongated areas for a given distance being greater than the number of groups of elongated parallel stripes for the same distance;

said index signals frequency of variation determined by the number of said first and second plurality of spaced parallel elongated areas scanned by said electron beam in said given time; and

signal processing means coupled to said circuit means comprising:

a first low-pass filter means coupled to said circuit means for separating said video information signal;

a second bandpass filter means coupled to said circuit means for separating said electrical carrier signals from said composite electrical signals;

third bandpass filter means coupled to said circuit means for separating said index signal from said composite electrical signals;

reference means coupled to said third bandpass filter means for deriving a reference wave having the same frequency as said electrical carrier signals; and

beat cancellation means coupled to said bandpass filter means for removing chosen frequencies from said video information signal.

l l. A television camera system according to claim wherein said signal processing means includes detector means coupled to said second bandpass filter means and said reference means for deriving color representative signals from said electrical carrier signal.

112. A television camera system according to claim llil wherein said signal processing means includes a trans lating means to include said heat cancellation means for deriving a composite color signal for transmission.

13. A television camera comprising:

an image pickup device including;

a transparent faceplate;

an electron gun operative to produce an electron beam;

an encoding filter comprising groups of elongated parallel stripes in each group having a different spectral response to light passing therethrough;

a layered target structure including a conductive signal electrode and a photoconductor layer addressed by said electron beam;

circuit means connected between said signal electrode and said electron gun to derive a composite electrical signal representative of light from an image directed upon said target, said composite electrical signal including video information signal representative of said image formed on said target, an electrical carrier signal having a frequency determined by the number of groups of said elongated parallel stripes scanned by said electron beam in a given time, and an index signal having a frequency lower than said carrier signal;

said target structure including a first plurality of spaced elongated parallel areas separated by a second plurality of spaced elongated parallel areas, the number of said areas in either of said plurality of areas being selected to produce current impulses of a frequency above the frequency of said electrical carrier signal when scanned by said electron beam traversely to the length of said areas, the width dimensions of said areas in one of said plurality of areas measured in the direction of electron beam scanning differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate which when scanned by said electron beam is at the frequency of said index signal.

it. A television camera according to claim l3 wherein:

the width dimensions in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is comprised of conducting material.

115. A television camera according to claim l3 wherein:

the width dimensions measured in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is nonconducting.

ll6. A television camera according to claim 13 wherein:

said first plurality of areas is comprised of conducting material and said second plurality of areas is nonconducting, the width dimensions measured in he direction of scanning of said first and second plulid rality of areas differ in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate.

117., A television camera according to claim lid wherein said first plurality of spaced parallel elongated areas is said conductive signal electrode.

lib. A television camera according to claim 17 wherein said target structure and said encoding filter being supported adjacent said transparent faceplate so that light from an image passes through said faceplate and said encoding filter before impinging on said target, the stripes of said encoding filter being positioned parallel to said first and second plurality of spaced parallel elongated areas wherein the number of spaced parallel elongated areas of said first and second plurality of spaced parallel elongated areas for a given distance being greater than the number of groups of said elongated parallel stripes for the same distance;

said indexing simials frequency of variation determined by the number of said first and second spaced parallel elongated areas scanned by said electron beam in said given time.

119. A television camera according to claim l8 wherein said encoding filter is a color encoding filter comprising color groups of elongated parallel stripes for encoding red, green and blue light.

2t). A television camera according to claim 18 wherein:

said color encoding filter comprises color groups of elongated parallel dichroic stripes for encoding red, green and blue light.

21. A television camera according to claim 19 wherein:

said color group is comprised of cyan, magenta and yellow parallel dichroic stripes.

22. A television camera comprising:

an image pickup device including;

a transparent faceplate;

an electron gun operative to produce an electron beam;

an encoding filter comprising groups of elongated parallel stripes in each group having a different spectral response to light passing therethrough;

a layered target structure including a conductive signal electrode and a photoconductor layer addressed by said electron beam;

circuit means connected between said signal electrode and said electron gun to derive a composite electrical signal representative of light from an image directed upon said target, said composite electrical signal including video information signal representative of said image formed on said target, an electrical carrier signal having a frequency determined by the number of groups of said elongated parallel stripes scanned by said electron beam in a given time, and an index signal having a frequency lower than said carrier signal;

said target structure including a first plurality of spaced elongated parallel areas separated by a sec ond plurality of spaced elongated parallel areas, the number of said areas in either of said plurality of areas being selected to produce current impulses of a frequency above the frequency of said electrical carrier signal when scanned by said electron beam traversely to the length of said areas, the width dimensions of said areas in one of said plurality of areas measured in the direction of electron beam scanning differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate whichwhen scanned by said electron beam is at the frequency of said index signal;

said target structure and said encoding filter being said index signals frequency of variation determined by the number of said first and second plurality of spaced parallel elongated areas scanned by said electron beam in said given time.

23. A television camera system comprising: an image pickup device comprising;

a faceplate;

an electron gun operative to produce an electron beam;

a layered target structure including a conductive signal electrode, said target structure including a first and second plurality of parallel elongated spaced areas, said first plurality of areas separated by said second plurality of areas, successive pairs of said first and second plurality of areas have different periods in the direction of scanning, said first plurality of parallel elongated spaced areas providing a first conductivity characteristic between said electron gun and said signal electrode and said second plurality of parallel elongated spaced areas providing a different conductivity characteristic between said electron gun and said signal electrode such that when said first and second plurality of areas are addressed by said electron beam an index signal is produced;

circuit means connected between said signal electrode and said electron gun to derive a video information signal representative of light from an image directed upon said target, said index signal comprised of current impulses resulting from the electron beam scanning across said first and second pluralities of parallel elongated spaced areas, the frequency of said current impulses being above the frequency range of said video signal information; and

means coupled to said circuit means for separating said index signal from said video signal information.

24. A television camera system according to claim 23 wherein a pair of said first and second areas, the ratio of said width of a first area to a width of said second area is not equal to the ratio of said corresponding widths in a successive pair of said first and second ar- 

2. A television camera system according to claim 1 wherein the width dimensions in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is comprised of conducting material.
 3. A television camera system according to claim 1 wherein the width dimensions measured in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is nonconducting.
 4. A television camera system according to claim 1 wherein: said first plurality of areas is comprised of conducting material and said second plurality of areas is nonconducting, the width dimensions measured in the direction of scanning of said first and second plurality of areas differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate.
 5. A television camera system according to claim 4 wherein said first plurality of spaced parallel elongated areas is said conductive signal electrode.
 6. A television camera system according to claim 5 wherein said target structure and said encoding filter being supported adjacent said transparent faceplate so that light from an image passes through said faceplate and said encoding filter before impinging on said target, the stripes of said encoding filter being positioned parallel to said first and second plurality of spaced parallel elongated areas wherein the number of spaced parallel elongated areas of said first and second plurality of spaced parallel elongated areas for a given distance being greater than the number of groups of said elongated parallel stripes for the same distance; said indexing signal''s frequency of variation determined by the number of said first and second spaced parallel elongated areas scanned by said electron beam in said given time; and signal processing means coupled to said means and said circuit means and responsive to said index signal for processing said composite electrical signal to derive a plurality of color representative signals.
 7. A television camera system according to claim 6 wherein said encoding filter is a color encoding filter comprising color groups of elongated parallel stripes for encoding red, green and blue light.
 8. a television camera system according to claim 6 wherein: said color encoding filter comprises color groups of elongated parallel dichroic stripes for encoding red, green and blue light.
 9. A television camera system according to claim 7 wherein: said color group is comprised of cyan, magenta and yellow parallel dichroic stripes.
 10. A television camera system comprising: an image pickup device including; a transparent faceplate; an electron gun operative to produce an electron beam; an encoding filter comprising groups of elongated parallel stripes in each group having a different spectral response to light passing therethrough; a layered target structure including a conductive signal electrode and a photoconduCtor layer addressed by said electron beam; circuit means connected between said signal electrode and said electron gun to derive a composite electrical signal representative of light from an image directed upon said target, said composite electrical signal including video information signal representative of said image formed on said target, an electrical carrier signal having a frequency determined by the number of groups of said elongated parallel stripes scanned by said electron beam in a given time, and an index signal having a frequency lower than said carrier signal; said target structure including a first plurality of spaced elongated parallel areas separated by a second plurality of spaced elongated parallel areas, the number of said areas in either of said plurality of areas being selected to produce current impulses of a frequency above the frequency of said electrical carrier signal when scanned by said electron beam traversely to the length of said areas, the width dimensions of said areas in one of said plurality of areas measured in the direction of electron beam scanning differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate which when scanned by said electron beam is at the frequency of said index signal; said target structure and said encoding filter being supported adjacent said transparent faceplate so that light from an image passes through said faceplate and said encoding filter before impinging on said target, the stripes of said encoding filter being positioned parallel to said first and second plurality of spaced parallel elongated areas, the number of spaced parallel elongated areas of said first and second plurality of spaced parallel elongated areas for a given distance being greater than the number of groups of elongated parallel stripes for the same distance; said index signal''s frequency of variation determined by the number of said first and second plurality of spaced parallel elongated areas scanned by said electron beam in said given time; and signal processing means coupled to said circuit means comprising: a first low-pass filter means coupled to said circuit means for separating said video information signal; a second bandpass filter means coupled to said circuit means for separating said electrical carrier signals from said composite electrical signals; third bandpass filter means coupled to said circuit means for separating said index signal from said composite electrical signals; reference means coupled to said third bandpass filter means for deriving a reference wave having the same frequency as said electrical carrier signals; and beat cancellation means coupled to said bandpass filter means for removing chosen frequencies from said video information signal.
 11. A television camera system according to claim 10 wherein said signal processing means includes detector means coupled to said second bandpass filter means and said reference means for deriving color representative signals from said electrical carrier signal.
 12. A television camera system according to claim 10 wherein said signal processing means includes a translating means to include said beat cancellation means for deriving a composite color signal for transmission.
 13. A television camera comprising: an image pickup device including; a transparent faceplate; an electron gun operative to produce an electron beam; an encoding filter comprising groups of elongated parallel stripes in each group having a different spectral response to light passing therethrough; a layered target structure including a conductive signal electrode and a photoconductor layer addressed by said electron beam; circuit means connected between said signal electrode and said electron gun to derive a composite electrical signal representative of light from an image directed upon said target, said composite electrical signal iNcluding video information signal representative of said image formed on said target, an electrical carrier signal having a frequency determined by the number of groups of said elongated parallel stripes scanned by said electron beam in a given time, and an index signal having a frequency lower than said carrier signal; said target structure including a first plurality of spaced elongated parallel areas separated by a second plurality of spaced elongated parallel areas, the number of said areas in either of said plurality of areas being selected to produce current impulses of a frequency above the frequency of said electrical carrier signal when scanned by said electron beam traversely to the length of said areas, the width dimensions of said areas in one of said plurality of areas measured in the direction of electron beam scanning differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate which when scanned by said electron beam is at the frequency of said index signal.
 14. A television camera according to claim 13 wherein: the width dimensions in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is comprised of conducting material.
 15. A television camera according to claim 13 wherein: the width dimensions measured in the direction of scanning of said first plurality of areas remains constant and said first plurality of areas is nonconducting.
 16. A television camera according to claim 13 wherein: said first plurality of areas is comprised of conducting material and said second plurality of areas is nonconducting, the width dimensions measured in he direction of scanning of said first and second plurality of areas differ in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate.
 17. A television camera according to claim 16 wherein said first plurality of spaced parallel elongated areas is said conductive signal electrode.
 18. A television camera according to claim 17 wherein said target structure and said encoding filter being supported adjacent said transparent faceplate so that light from an image passes through said faceplate and said encoding filter before impinging on said target, the stripes of said encoding filter being positioned parallel to said first and second plurality of spaced parallel elongated areas wherein the number of spaced parallel elongated areas of said first and second plurality of spaced parallel elongated areas for a given distance being greater than the number of groups of said elongated parallel stripes for the same distance; said indexing signal''s frequency of variation determined by the number of said first and second spaced parallel elongated areas scanned by said electron beam in said given time.
 19. A television camera according to claim 18 wherein said encoding filter is a color encoding filter comprising color groups of elongated parallel stripes for encoding red, green and blue light.
 20. A television camera according to claim 18 wherein: said color encoding filter comprises color groups of elongated parallel dichroic stripes for encoding red, green and blue light.
 21. A television camera according to claim 19 wherein: said color group is comprised of cyan, magenta and yellow parallel dichroic stripes.
 22. A television camera comprising: an image pickup device including; a transparent faceplate; an electron gun operative to produce an electron beam; an encoding filter comprising groups of elongated parallel stripes in each group having a different spectral response to light passing therethrough; a layered target structure including a conductive signal electrode and a photoconductor layer addressed by said electron beam; circuit means connected between said signal electrode and said electron gun to derive a composite electricAl signal representative of light from an image directed upon said target, said composite electrical signal including video information signal representative of said image formed on said target, an electrical carrier signal having a frequency determined by the number of groups of said elongated parallel stripes scanned by said electron beam in a given time, and an index signal having a frequency lower than said carrier signal; said target structure including a first plurality of spaced elongated parallel areas separated by a second plurality of spaced elongated parallel areas, the number of said areas in either of said plurality of areas being selected to produce current impulses of a frequency above the frequency of said electrical carrier signal when scanned by said electron beam traversely to the length of said areas, the width dimensions of said areas in one of said plurality of areas measured in the direction of electron beam scanning differing in a progression from smaller widths to progressively larger widths and progressively back to smaller widths at a cyclical rate which when scanned by said electron beam is at the frequency of said index signal; said target structure and said encoding filter being supported adjacent said transparent faceplate so that light from an image passes through said faceplate and said encoding filter before impinging on said target, the stripes of said encoding filter being positioned parallel to said first and second plurality of spaced parallel elongated areas, the number of spaced parallel elongated areas of said first and second plurality of spaced parallel elongated areas for a given distance being greater than the number of groups of elongated parallel stripes for the same distance; said index signal''s frequency of variation determined by the number of said first and second plurality of spaced parallel elongated areas scanned by said electron beam in said given time.
 23. A television camera system comprising: an image pickup device comprising; a faceplate; an electron gun operative to produce an electron beam; a layered target structure including a conductive signal electrode, said target structure including a first and second plurality of parallel elongated spaced areas, said first plurality of areas separated by said second plurality of areas, successive pairs of said first and second plurality of areas have different periods in the direction of scanning, said first plurality of parallel elongated spaced areas providing a first conductivity characteristic between said electron gun and said signal electrode and said second plurality of parallel elongated spaced areas providing a different conductivity characteristic between said electron gun and said signal electrode such that when said first and second plurality of areas are addressed by said electron beam an index signal is produced; circuit means connected between said signal electrode and said electron gun to derive a video information signal representative of light from an image directed upon said target, said index signal comprised of current impulses resulting from the electron beam scanning across said first and second pluralities of parallel elongated spaced areas, the frequency of said current impulses being above the frequency range of said video signal information; and means coupled to said circuit means for separating said index signal from said video signal information.
 24. A television camera system according to claim 23 wherein a pair of said first and second areas, the ratio of said width of a first area to a width of said second area is not equal to the ratio of said corresponding widths in a successive pair of said first and second areas. 